(Keynote) Oxide Semiconductors, Solid-State Chemistry, and Photoelectrochemistry: A Nexus

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Solid-state chemistry languished as an esoteric discipline till interest exploded on the so-called high-Tc superconductor materials; oxides were discovered to have unique properties in this regard. Paralleling this was the gradual realization that solid-state chemistry principles underpinned many technologically-important areas such as batteries, supercapacitors, and even solar cells. The culmination of this trend was in the application of solid-state chemistry to the preparation and characterization of electrode materials in photoelectrochemical (PEC) cells. This perspective talk will examine how solid-state chemistry principles have contributed both to the design and synthesis of photoelectrode materials for PEC applications related to water splitting, CO2 reduction, and environmental remediation. The design of new-generation oxide semiconductors with the correct optoelectronic and bulk/interfacial chemistry characteristics needed to efficiently drive the above reactions will be addressed. The list of material pre-requisites for efficient solar fuels generation or photocatalytic degradation is daunting and it is hardly surprising that a “magic bullet” material has not emerged even after 4 decades of R&D effort. However, these same challenges have attracted researchers drawn from diverse communities including solid-state/device physics, photophysics/photochemistry, colloid chemistry, ultra-fast spectroscopy, classical inorganic chemistry, environmental chemistry and organometallics. To keep the discussion coherent, only a very limited subset of topics will be addressed in this talk. The progression from binary to ternary, and even quaternary oxides will be examined from the perspective of “band-gap engineering” (a much-maligned word!) and tuning of the interfacial semiconductor surface/fluid energetics. Examples will be drawn from recent research in the speaker’s laboratory and with collaborators.1-4 Acknowledgements The author thanks his collaborators, particularly, Prof. Csaba Janaky (University of Szeged, Hungary) and the National Science Foundation (CHE- 1303803) for partial funding support.